Modulator circuit



J. c. HANSEN 2,449,998

MODULITOR CIRCUIT Filed July 22, 1943 Se t. 28, 1948..

MODULATOR "osclLLATo INVENTOR. JOHN C. HANSEN.

AT TORNE Y Patented Sept. 28, 1948 UNITED STATES PATENT OFFICE .monnmroaciacorr John C. Hansen, Avon, N. J. Application July 22, 1943, SerialNo. 495,117

(c1. 250-27) (Granted under the act of .March 3, 1883, as

Claims.

1 v The invention described herein may be manuf-actured and used by orfor the Government for governmental purposes, without the payment to meof any royalty thereon.

This invention relates to electron tube modulating networks,particularly the application of such networks for pulse modulating thetransmitter of pulse-echo object detection equipment.

The tubes of such transmitters are usually maintained at cutoff byv ahigh negative bias impressed upon the grids, or insufficient potentialon the plates. Sharp positive pulses of high peak power, developed in amodulator, are impressed on said grids to overcome said bias, or on saidplates to raise their potential, sothat the transmitter oscillates forthe duration of said pulses. Such oscillating periods are of relativelyshort duration separated by intervals of considerably longer duration. V7 Reference is made to the application of James R. Moore, Serial No.495,718, filed on even date herewith, directed to a modulator whichconsumes a substantial amount of power only while the transmitter isbeing pulsed. This is accomplished by using in the output circuit of themodulator tube an electronic impedance which. is varied simultaneouslywith, and in opposite sense as, the impedance of the modulator tube.

It is an object of the present invention, generally, to improve theinventiondisclosed in the Moore application above referred -:t0. This isdone by providing more rapid and effective means for oppositely varyingthe conductivities of the modulator impedances'so that sharper pulsescan be generated.

For a better understanding of the invention, together with other andfurther objects thereof, reierence is had to the following descriptiontaken in connection with the v accompanying drawing, and its scope willbe pointed out in the accompanying claims.

Referring to the drawing, which shows a sc'he matic circuit of myinvention, tubes and [2 are part of a conventional transmitter.oscillator, the usual plate potential sources and tuning and couplingelements being omitted. Said tubes are normally blocked by means of anegative potential, impressed upon the grids thereof, from a potentialsource l3 through a high resistance [4. Said tubes are adapted to beintermittently unblocked by means of sharp positive pulses of voltageimpressed upon the grids in such direction as to overcome said negativebias, so that the oscillator functions for the duration of said pulses.

The pulses are derived from the output circuit amended April 30,1928:1370 o. G. 757) 2 of a modulator network comprising two tubes f5and I6 having their space current paths con nected in series with aresistor IT, a choke l8, and a source of high potential 13 voltage l9.condenser 20 shunts resistor l1; Tube [6 is also con nected to a secondsource of B voltage 2| in series with a diode 22, resistor l1, and chokel8. source 2| is of considerably lower voltage than source I9. The gridof tube 15 is also biased positively from source 2| through a highresistance 23.- A separate biasing source may be used if desired;Terminal 24 is adapted tobe connected to a source of intermittentlygenerated negative going pulses of short duration spaced at intervals orconsiderably longer duration. These pulses are impressed on the grid oftube It through a blocking condenser 25, of low impedance to the pulseenergy.- 1 Either end of choke It! can be coupled to the grids ofoscillator tubes 10 and I2 through a two position switch 26 and ablocking condenser 21, of low impedance .to the pulse energy. I

The above described circuit operates as follows: Since there is apositive grid bias impressed on tube It, said tube is highly conductinganda large current flows from source 2 I, through diode 22, resistor ll,choke l8, the anode-cathode path of tube l6, and then back to the sourcethrough ground. This current builds up an intense magnetic field inchoke IS.

The voltage drop across resistor I1 and choke l8 biases the grid of tube15 negatively with respect to its cathode, so that said tube operates ator below plate current cutoff and no current can. flow therethrough fromsource 19. Under these conditions,- tube l5 constitutes, in efiect, a.load-of substantially infinite impedance in the anodecircuit of tube l6so that no poweris dissipated by source 19. 1

The grid of tube 16 is intermittently rendered negative by the pulsesimpressed thereon from terminal 24. Each pulse blocks tube l6 so thatthe current through resistor l! and choke I8 is reduced to zero. As aresult, the blocking bias on the grid of tube I5 is removed and inaddition, a strong positive voltage, generated by the sudden collapse ofthe field in the choke, is ap' plied to said grid,- whereby theimpedance of said 'tubezis suddenly reduced to an extremely low.

value. The decay .of the negative biasing voltage is determined by thetime constant of resistor l1 and condenser 20.

This causes the potential at the cathode of tube IE to risesubstantially to the potential of the anode of. said tube; and a suddensurge of current takes place from source l9, through tube l5, resistor[1, switch 26, blocking condenser 21, of low impedance to the pulsevoltage, and resistor [4 to ground. The direction of this current issuch as to bias the grids of the oscillator tubes highly positive inopposition to the negative bias of source l3. Diode 22 preventsdissipation of this voltage to ground. As a result, the oscillator gridsare rendered sufficiently positive to cause the oscillator to generatehigh frequency oscillations for the duration of each pulse. The cycle ofoperations above described are repeated for each negative pulse appliedto the grid of tube Hi. If plate modulation is used, then the output ofthe modulator will obviously be applied to the plates of the oscillator.

Switch 26 is connected to the upper position, as shown, because the loadpresented by the oscillator is assumed to be of low impedance. Undersuch condition, connection to the lower end of the choke would tend toshunt out the high positivepotential developed by the collapsing fieldin the choke.

In the case where the impedance presented by the oscillator is high,switch 26 may be moved to the lower position, so that the high positivevoltage developed in the choke is also impressed on the oscillator gridsso as to add to the effect obtained from tube I5.

It will be seen that relatively little power is dissipated by themodulator during the intervals between pulses, even though tube 16 isconducting. The combined resistance of resistor l1 and choke i8 is ofthe order of a few hundred ohms and the voltage of source I9 is smallcompared to the voltage of source 2|. Hence the power dissipated betweenpulse intervals is relatively low compared to the peak power developedin the circuit.

While there has been described what is at present considered a preferredembodiment of the invention, it will be obvious to those skilled in theart that various changes and modifications may be made therein withoutdeparting from the invention, and it is, therefore, aimed in theappended claims, to cover all such changes and modifications as fallwithin the true spirit and scope of the invention.

I claim:

1. A network comprising a first grid-controlled electron tube and meansin its grid circuit to vary the impedance thereof, a secondgrid-controlled electron tube, a first circuit including a source ofpotential, the anode-cathode path of said second grid-controlledelectron tube, a choke, and the anode-cathode path of said first tube,all connected in a closed series circuit in the order named, a secondcircuit exclusive of said second electron tube and including a source ofpotential, said choke, and said anode-cathode path of said first tube,all in a closed series circuit in the order named, a connection from theanode of said first tube to the grid of said second tube, and an outputcircuit coupled to a terminal of said choke.

2. A network comprising a first grid-controlled electron tube and meansin its grid circuit to vary the impedance'thereof, a secondgrid-controlled electron tube, a first circuit including a source ofpotential, the anode-cathode path of said second grid-controlledelectron tube, a resistor, a choke, and the anode-cathode path of saidfirst tube, all connected in a closed series circuit in the order named,a second circuit including a second source of potential, a diode,

said resistor, said choke, and said anode-cathode path of said firsttube, all in a closed series circuit in the order named, a connectionfrom the anode of said first tube to the grid of said second tube, anoutput circuit, and means to couple the latter to either terminal ofsaid choke.

I 3. An electron tube network comprising a diode, first and secondelectron tubes each having at least an anode, cathode and grid, aresistor having one end connected to the cathodes of said diode and saidfirst tube and the other end connected to one end of a choke, the otherend of said choke being connected to the anode of said second tube aidthe grid of said first tube, means to impress steady positive potentialsupon the anodes of said diode and said first tube, with reference to thecathode of said second tube, said second tube being normally conductingwhereby a current flows through said diode, said resistor, said chokeand said second tube, and whereby the resulting voltage drop across saidresistor biases the grid of said first tube negative, means to vary theconductivity said second tube, an output circuit and means to couplesaid output circuit between the cathode of said first tube and the anodeof said second tube.

4. An electronic network comprising a diode, first and second electrontubes each having at least an anode, cathode and grid, a resistor havingone end connected to the cathodes of said diode and said first electrontube and the other end connected to one end of a choke, the other end ofsaid choke being connected to the anode of said second tube and the gridof said first tube, means to impress steady positive potentials upon theanodes of said diode and said first tube, with reference to the cathodeof said second tube said second tube being normally conducting whereby acurrent flows through said diode, said resistor, said choke and saidsecond tube, and whereby the resulting voltage drop across said resistormaintains the grid of said first tube sufiiciently negative to render itnon-conducting, means to render said second tube momentarilynon-conducting, whereby said voltage drop is decreased and the currentthrough said choke is interrupted, means responsive to said interruptionto render said first tube highly conducting so that the positivepotential of its cathode is increased, and a high impedance load circuitcoupled' to the junction of said choke and the anode of said secondtube.

5. An electron tube network comprising a diode, first and secondelectron tubes each having at least an anode, a cathode and grid, aresistor having one end connected to the cathodes of said diode and said,first electron tube and the other end connected to one end of a choke,the other end of said choke being connected to the anode of said secondelectron tube and the grid of said first tube, means to impress steadypositive potentials upon the anodes of said diode and said firstelectron tube with reference to the cathode of said second tube, saidsecond tube being normally conducting whereby a current flows throughsaid diode, said resistor, said choke, and said second tube, and wherebythe resulting volt-age drop across said resistor maintains the grid ofsaid first tube sufficiently negative to render it non-conducting, meansto render said second tube momentarily non-conducting, whereby saidvoltage drop is decreased and the current through said choke isinterrupted, means responsive to said interruption to render said firsttube highly conducting so that the positive potential of its cathode isincreased, and a low impedance load circuit coupled to the junction ofsaid choke and said resistor.

JOHN C. HANSEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

Number Number 10 400,976

Name Date Wilson Nov. 12, 1940 Wilson Nov. 12, 1940 White Apr. 28, 1942Clough July 7, 1942 Lindquist Sept. 15, 1942 FOREIGN PATENTS CountryDate Great Britain Nov. 6, 1933

